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Narrow-band Green Emitting Nitridolithoalumosilicate Ba[Li2(Al2Si2)N6]:Eu2+ with Framework Topology whj for LED/LCD-Backlighting Applications Philipp Strobel, Sebastian Schmiechen, Markus Siegert, Andreas Tücks, Peter J Schmidt, and Wolfgang Schnick Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.5b02702 • Publication Date (Web): 19 Aug 2015 Downloaded from http://pubs.acs.org on August 19, 2015
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Chemistry of Materials
Narrow-band Green Emitting Nitridolithoalumosilicate Ba[Li2(Al2Si2)N6]:Eu2+ with Framework Topology whj for LED/LCD-Backlighting Applications Philipp Strobel,† Sebastian Schmiechen,† Markus Siegert,† Andreas Tücks,‡ Peter J. Schmidt,‡ and Wolfgang Schnick*,† †
Department of Chemistry, University of Munich (LMU), Butenandtstrasse 5-13, 81377 Munich, Germany
‡
Lumileds Germany GmbH, Lumileds Development Center Aachen, Philipsstrasse 8, 52068 Aachen, Germany
ABSTRACT: Eu2+- as well as Ce3+-doped Ba[Li2(Al2Si2)N6] and its related Mg-substituted compounds Ba[(Mg2-xLix)(Al4-xSix)N6]:Eu2+ (x = 0-2) with x = 1.6, 1.8 have been synthesized by metathesis reactions in tantalum ampules. Crystal structures were solved and refined from single-crystal X-ray diffraction data. All three compounds crystallize in tetragonal space group P4/ncc (no. 130) (Z = 4, Ba[Li2(Al2Si2)N6]:Eu2+: a = 7.8282(4), c = 9.9557(5) Å, R1 = 0.0144, wR2 = 0.0366). Their crystal structures, exhibiting the novel framework topology whj, consist of a highly condensated anionic tetrahedra network of disordered (Li/Mg)N4 and (Al/Si)N4 units, connected to each other by common edges and corners. The degree of condensation (i.e. atomic ratio (Al,Li,Mg,Si):N) is κ = 1. The Ba2+-position is coordinated eightfold by N3- in form of a truncated square pyramid. Upon doping with Eu2+ narrow-band emission in the green to yellow spectral range is observed (λem = 532 - 562 nm, fwhm ∼1962 cm-1). Ce3+-doped crystals of Ba[Li2(Al2Si2)N6] show blue emission (λem = 468; 507 nm). According to the tunability of the narrow-band green emission, application in LED-backlight LCDs appears promising.
INTRODUCTION The quest for even thinner and lighter modern highcontrast LCDs (liquid crystal displays) with applications in televisions and portable devices demands replacement of common cold cathode fluorescent lamps (CCFLs) by solid-state LEDs (light-emitting diodes).1,2 Highly efficient phosphor converted (pc-)LEDs combine very desirable properties like fast switching time and dimming as well as no turn-on delay. They allow construction of flat displays and are environmentally friendly, showing low energy consumption.3 Phosphor converted LEDs currently used in LCDs consist of highly efficient blue-emitting (In,Ga)N-LEDs and the yellow emitting phosphor Y3−xGdxAl5−yGayO12:Ce3+ (YAG:Ce). To improve emission quality, red and green luminophors are discussed to replace this broad-band yellow phosphor.4 Exploiting narrow-band emitting luminescent materials reduces LED emission that need to be excluded by filters. To achieve a brilliant image with high color saturation, narrow-band emission especially in the green spectral region is mandatory.5 This leads to a huge demand for innovative narrow-band green and red emitting luminescent materials. Recently, we have reported on next generation Eu2+-doped narrow-band red-emitting phosphors, the nitridolithoaluminate Sr[LiAl3N4]:Eu2+ (SLA) and the nitridomagnesosilicate Sr[Mg3SiN4]:Eu2+ (SMS). SLA shows narrow-band
emission at 650 nm with fwhm (full width at half maximum) of ∼1180 cm-1 (∼50 nm), SMS exhibits even narrower emission with fwhm of only 1170 cm-1 (∼43 nm, λem = 615 nm).6-8 Examples for green Eu2+ phosphors are (Ba,Sr)2SiO4:Eu2+ and the oxonitridosilicate SrSi2O2N2:Eu2+. The latter exhibits an emission maximum of 535 nm with fwhm ∼2600 cm-1.9,10 β-SiAlON:Eu2+ is currently the most promising green phosphor for backlighting applications in high gamut displays. It shows emission at 528-550 nm (fwhm ∼1760 cm-1). However, its external quantum efficiency is limited (EQE 80%. To improve color saturation the discovery of green phosphors that meet the requirements mentioned above is of high relevance. In this contribution we describe syntheses and characterization of the nitridolitho(magneso)alumosilicates Ba[(Mg2-xLix)(Al4-xSix)N6] (x = 0-2) with x = 1.6, 1.8 and 2.0. The respective Eu2+-doped materials show promising luminescence properties in the green to yellow region of the visible spectrum under blue light irradiation, making them promising candidates for implementation in white pc-LEDs for LCD backlighting applications.11
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EXPERIMENTAL SECTION Synthesis. All experiments were carried out in argonfilled glove boxes (Unilab, MBraun, Garching, O2
